Electrical conductors, production methods thereof, and electronic devices including the same

ABSTRACT

An electrical conductor includes: a first conductive layer including a plurality of ruthenium oxide nanosheets, wherein at least one ruthenium oxide nanosheet of the plurality of ruthenium oxide nanosheets includes a halogen, a chalcogen, a Group 15 element, or a combination thereof on a surface of the ruthenium oxide nanosheet.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 15/296,261, filed on Oct. 18, 2016, which claimspriority to and the benefit of Korean Patent Application No.10-2015-0145636, filed in the Korean Intellectual Property Office onOct. 19, 2015, and all the benefits accruing therefrom under 35 U.S.C. §119, the entire contents of which in their entirety are incorporatedherein by reference.

BACKGROUND 1. Field

An electrical conductor, a method of producing the electrical conductor,and a device including the same are disclosed.

2. Description of the Related Art

An electronic device, such as a flat panel display, a liquid crystaldisplay (LCD), a light emitting diode (LED) display, a touch screenpanel, a solar cell, a transparent transistor, and the like, may includean electrically conductive thin film such as a transparent electricallyconductive thin film. It is desirable for a material of an electricallyconductive film to have high light transmittance (e.g., greater than orequal to about 80 percent (%) in a visible light region) and lowspecific resistance (e.g., less than or equal to about 1×10⁻⁴ohm·centimeter (Ω·cm)). Currently available materials used intransparent electrically conductive thin films include indium tin oxide(ITO), tin oxide (SnO₂), zinc oxide (ZnO), and the like. ITO is atransparent electrode material and is a transparent semiconductor havinga wide bandgap of 3.75 electron volts (eV), and may be used tomanufacture conductive films having a large surface area using asputtering process. However, in terms of application to a flexible touchpanel or a UD-grade high resolution display, ITO has poor flexibilityand will inevitably cost more due to limited reserves of indium.Therefore, development of an alternative material is desired.

Recently, a flexible electronic device, e.g., a foldable or bendableelectronic device, has been drawing attention as a next generationelectronic device. Therefore, there is a need for a material havingimproved transparency, relatively high electrical conductivity, andsuitable flexibility, as a transparent electrode material.

SUMMARY

An embodiment provides a flexible electrical conductor having improvedconductivity and improved light transmittance.

Another embodiment provides a method of producing the electricalconductor.

Yet another embodiment provides an electronic device including theelectrical conductor.

In an embodiment, an electrical conductor includes: a first conductivelayer including a plurality of ruthenium oxide nanosheets, wherein atleast one ruthenium oxide nanosheet of the plurality of ruthenium oxidenanosheets is surface-doped with any of a halogen, a chalcogen, a Group15 element, and a combination thereof.

The halogen may be selected from F, Cl, Br, I, and a combinationthereof.

The chalcogen may be selected from S, Se, Te, and a combination thereof.

The Group 15 element may be selected from N, P, As, and a combinationthereof.

The halogen, the chalcogen, and the Group 15 element may be present asan ionic species, a surface-bound reactive group, an oxyhalide, an oxychalcogenide, or a combination thereof.

The electrical conductor may include a second conductive layer that isdisposed on a first surface of the first conductive layer and includes aplurality of conductive metal nanowires.

The plurality of conductive metal nanowire may include silver (Ag),copper (Cu), gold (Au), aluminum (Al), cobalt (Co), palladium (Pd), or acombination thereof.

The plurality of conductive metal nanowires may have an average diameterof less than or equal to about 50 nanometers (nm) and an average lengthof greater than or equal to about 1 micrometer (um).

The electrical conductor may be a transparent conductive film.

The plurality of ruthenium oxide nanosheets may have an average lateralsize of greater than or equal to about 0.1 micrometer (μm) and less thanor equal to about 100 μm.

The ruthenium oxide nanosheets may have a thickness of less than orequal to about 3 nanometers (nm).

The first conductive layer may be a discontinuous layer including anopen space disposed between neighboring ruthenium oxide nanosheets of atleast two ruthenium oxide nanosheets of the plurality of ruthenium oxidenanosheets, and an area of the open space may be less than or equal toabout 50% of a total area of the first conductive layer.

The electrical conductor may have transmittance of greater than or equalto about 85% with respect to light having a wavelength of 550 nm or withrespect to visible light having a wavelength of about 400 nm to 700 nm(for example, when the first and/or conductive layer(s) have a thicknessof 100 nm or less, e.g., less than or equal to about 90 nm, less than orequal to about 80 nm, less than or equal to about 70 nm, less than orequal to about 60 nm, or less than or equal to about 50 nm).

The electrical conductor may have sheet resistance of less than or equalto about 1.2×10⁴ ohms per square (Ω/sq), for example, less than or equalto about 1×10⁴ ohms per square.

At least one of the first conductive layer and the second conductivelayer may further include a binder.

The electrical conductor may further include an overcoating layerincluding a thermosetting resin, an ultraviolet light-curable resin, ora combination thereof, and wherein the overcoating layer is disposed onat least one of the first conductive layer and the second conductivelayer.

The electrical conductor may further include a transparent substratedisposed on an opposite second surface of the first conductive layer.

In some embodiments, a method of producing the electrical conductorincludes: heat-treating a mixture of a ruthenium oxide and an alkalimetal compound to prepare an alkali metal-substituted layered rutheniumoxide;

treating the alkali metal-substituted layered ruthenium oxide with anacidic solution to prepare a proton exchanged layered ruthenium oxide,wherein at least a portion of the alkali metal is replaced with aproton;

contacting the proton exchanged layered ruthenium oxide with a C1 to C20(e.g., C1 to C16) alkyl ammonium compound to prepare a C1 to C20 (e.g.,C1 to C16) alkyl ammonium-layered ruthenium oxide; and

mixing the C1 to C20 (e.g., C1 to C16) alkyl ammonium-layered rutheniumoxide with a solvent to obtain an exfoliated ruthenium oxide nanosheet,

wherein the method further includes conducting a surface doping toobtain a plurality of surface-doped ruthenium oxide nanosheets, and

wherein the surface doping comprises adding the alkali metal-substitutedlayered ruthenium oxide, the proton exchanged layered ruthenium oxide,or the exfoliated ruthenium oxide nanosheet to an aqueous solutionincluding a ruthenium halide, a ruthenium chalcogenide, an alkali metalhalide, an ammonium halide, or a ruthenium-Group 15 element compound toform a mixture, and heating the mixture at a temperature of greater thanor equal to about 100° C.

The surface doping is conducted with respect to the alkali metalsubstituted layered ruthenium oxide, and the method may further includedrying a surface-doped product.

The surface doping is conducted with respect to the exfoliated rutheniumoxide nanosheets, and the method may further include dispersing asurface-doped product in a mixture of a solvent and a C1 to C20 (e.g.,C1 to C16) alkyl ammonium compound to prepare a re-exfoliated rutheniumoxide nanosheet.

In another embodiment, an electronic device including the electricalconductor is provided.

The electronic device may be a flat panel display, a touch screen panel,a solar cell, an e-window, an electrochromic mirror, a heat mirror, atransparent transistor, or a flexible display.

According to an embodiment, a surface of a ruthenium oxide nanosheet isthermochemically doped with a halogen, a chalcogen, or a Group 15element to enhance an electrical conductivity thereof. When theaforementioned element is doped on the ruthenium oxide nanosheet via asurface reaction, the nanosheets may provide increased electricalconductivity and enhanced light transmittance and thereby may be used ina flexible or foldable display electrode material.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of this disclosure willbecome more apparent by describing in further detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1A is a schematic illustration of a process for the production ofan electrical conductor, in accordance with an embodiment;

FIG. 1B is a schematic illustration of a process for the production ofan electrical conductor, in accordance with another embodiment;

FIG. 10 is a schematic illustration of a process for the production ofan electrical conductor, in accordance with still another embodiment;

FIG. 2 is a schematic illustration of a structure of a surface-dopedruthenium oxide nanosheet as confirmed by a computer simulation, wherein1 denotes an halogen atom, a chalcogen atom, or a Group 15 atom, 2denotes an oxygen atom, and 3 denotes a ruthenium atom;

FIG. 3 is a schematic cross-sectional view of a touch screen panel foran electronic device, according to an embodiment;

FIG. 4A is a scanning electron microscope (SEM) image of a protonatedruthenium oxide in Example 1 prior to being treated with RuCl₃;

FIG. 4B is a graph of intensity (arbitrary units, a.u.) versus energy(kiloelectron volts, keV) showing the results of energy dispersive X-rayspectroscopy (EDX) analysis of the protonated ruthenium oxide in FIG.4A;

FIG. 5 is a graph of normalized intensity versus diffraction angle(degrees two-theta (2⊖)) showing the results of X-ray diffractionanalysis of the protonated ruthenium oxide in Example 1 prior to (lower)and after (upper) being treated with RuCl₃;

FIG. 6A is an SEM image of protonated ruthenium oxide in Example 1 afterbeing treated with RuCl₃;

FIG. 6B is a graph of intensity (arbitrary units, a.u.) versus energy(kiloelectron volts, keV) showing the results of an EDX analysis of theprotonated ruthenium oxide in FIG. 6A;

FIG. 7 is a graph of sheet resistance (ohms per square, Ω/sq) versustransmittance (percent, %) for each of the electrical conductorsprepared in Example 1 and Comparative Example 1, respectively; and

FIG. 8 is a graph of intensity (a.u.) versus binding energy (electronvolts, eV) showing the results of X-ray photoelectron spectroscopy (XPS)analysis of the first layer prepared in Example 1 and ComparativeExample 1.

DETAILED DESCRIPTION

Advantages and characteristics of this disclosure, and a method forachieving the same, will become evident by referring to the followingexemplary embodiments together with the drawings attached hereto.However, this disclosure may be embodied in many different forms and isnot to be construed as limited to the embodiments set forth herein. Ifnot defined otherwise, all terms (including technical and scientificterms) in the specification may be defined as those commonly understoodby one skilled in the art. The terms defined in a dictionary are not tobe interpreted ideally or exaggeratedly unless clearly definedotherwise. In addition, unless explicitly described to the contrary, theword “comprise” and variations such as “comprises” or “comprising” willbe understood to imply the inclusion of stated elements but not theexclusion of any other elements.

Further, the singular includes the plural unless mentioned otherwise.

In the drawings, the thickness of layers, regions, etc., are exaggeratedfor clarity. Like reference numerals designate like elements throughoutthe specification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

As used herein, the phrase “a first element is disposed on a secondelement” means that the first element is adjacent to (e.g., is incontact with) the second element and the upper and lower positiontherebetween is not limited.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting to “a” or“an.” “or” means “and/or.” As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (e.g., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±10%, or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may have rough and/or nonlinear features. Moreover, sharp anglesthat are illustrated may be rounded. Thus, the regions illustrated inthe figures are schematic in nature and their shapes are not intended toillustrate the precise shape of a region and are not intended to limitthe scope of the present claims.

As used herein, the term “sheet resistance” refers to a value determinedby a 4-point probe method for a specimen having a predetermined size(e.g., 210 mm×297 mm).

As used herein, a transmittance of a material is the value excludinglight absorption of a substrate. As used herein, the transmittance mayrefer to a transmittance with respect to visible light having awavelength of about 400 nm to 800 nm or with respect to light having awavelength of about 550 nm.

As used herein, the term “ionic species” refers to an element which ispresent in an ionized form. For example, in the case of a halogen or achalcogen (e.g., a Group 16 element), the ionic species may be F⁻, Cl⁻Br⁻, I⁻, Se²⁻, S²⁻, Te²⁻, and the like. The ionic species may be boundto an oxygen atom or to a ruthenium atom on a surface of the nanosheet.

As used herein, the term “surface bound reactive group” refers to anionic species that forms a bond with an oxygen atom or with a rutheniumatom on the surface of the nanosheet.

As used herein, the term “surface doping” or “surface-doped” refers to amaterial in which a doping element, such as a halogen, a chalcogen, or aGroup 15 element, forms a chemical or physical bond, such as a covalentbond, an ionic bond, a hydrogen bond, a van der Waals bond, or the like,with an oxide (e.g., an oxygen atom or a ruthenium atom) on a surface ofthe nanosheet and such that the doping element is not separated from thesurface of the nanosheet via physical manipulation, such as dispersingor agitation in water or a water miscible solvent (e.g., alcohol and thelike). For example, the surface-doped ruthenium oxide nanosheet mayinclude the doping element on a surface thereof.

In an embodiment, an electrical conductor includes a first conductivelayer including a plurality of ruthenium oxide nanosheets. In theelectrical conductor, at least two of ruthenium oxide nanosheets are incontact with one another to provide an electrical connection (e.g.,electrical conduction path). As used herein, “the nanosheets being incontact with one another to provide an electrical connection (e.g., theelectrically conduction path)” refers to the case where the contactbetween the nanosheets is made to provide an electrical conduction path,and thereby the conductive layer has an electrical conductivity (forexample, of a sheet resistance of less than or equal to about 1,000,000ohm/sq.). At least one of the ruthenium oxide nanosheet is surface-dopedwith a halogen, a chalcogen, a Group 15 element, or a combinationthereof.

The ruthenium oxide may form a nanosheet when it is exfoliated byintercalation. The ruthenium oxide nanosheet thus prepared may be usedin an electrical conductor (e.g., to provide a transparent electrodematerial). As used herein, the term “ruthenium oxide” refers to amaterial represented by the formula RuO_(2+x), wherein x is 0 to 0.5.

The ruthenium oxide nanosheet may be prepared by any suitable method.Referring to FIGS. 1A to 1C, a bulk material for producing a rutheniumoxide nanosheet may be prepared from an alkali metal ruthenium oxide(e.g., an alkaline metal ruthenium oxide of the formula MRuO₂, wherein Mis Na, K, Rb, or Cs), which has a layered structure (for example astructure of the formula M-RuO₂-M-RuO₂-M for the alkali metal rutheniumoxide). The alkali metal ruthenium oxide may be obtained by mixing analkali metal compound with ruthenium oxide and calcining or melting theobtained mixture at an appropriate temperature, for example at about500° C. to about 1000° C., for at least about 1 hour (h) or longer,(e.g., for at least about 6 h). The alkali metal ruthenium oxide is thenwashed with water to obtain a hydrate of the alkali metal rutheniumoxide (e.g., M_(a)RuO_(2+x)nH₂O, wherein a is 0 to about 0.3, x is 0 toabout 0.5, and n is a number that denotes the hydration state, and isnot particularly limited and for example, may be about 0.1 to about0.9).

When the obtained hydrate of the alkali metal ruthenium oxide is treatedwith an acid solution, at least a portion of the alkali metal undergoesa proton-exchange to provide a proton-type alkali metal ruthenatehydrate (e.g., having a formula H_(a)RuO_(2+x)nH₂O, where x=0 to about0.5, and a is 0 to about 0.3, when all the alkali metal undergoes aproton-exchange).

The obtained proton-exchanged alkali metal ruthenate hydrate may becontacted with a C1 to C20 (e.g., C1 to C16) alkyl ammonium or a C1 toC20 (e.g., C1 to C16) alkylamine to prepare a C1 to C20 (e.g., C1 toC16) alkyl ammonium- or a C1 to C20 (e.g., C1 to C16)alkylamine-substituted compound, which is then mixed with a solvent toobtain exfoliated ruthenium oxide nanosheets.

The solvent may be a high dielectric constant solvent. For example, thesolvent may include water, alcohol, acetonitrile, dimethyl sulfoxide,dimethyl formamide, propylene carbonate, or a combination thereof.

For example, during the protonation of Na_(a)RuO_(2+x), Na_(a)RuO_(2+x)and an acid compound (e.g., HCl) react with one another, and thereby Na⁺is substituted with H⁺ to prepare a protonated layered ruthenium oxide(e.g., H_(a)RuO_(2+x)). Subsequently, the H_(a)RuO_(2+x) may be reactedwith an alkyl ammonium salt intercalant (e.g., tetraalkyl ammoniumhydroxide), so that H⁺ may be replaced with an alkyl ammonium (e.g.,tetrabutylammonium, TBA⁺). The alkyl ammonium salt may be a C1 to C20alkyl ammonium salt. Without being limited by theory, it is believedthat the intercalant (e.g., TBA⁺) has such a large size that when it isinterposed between the H_(a)RuO_(2+x) layers, an interlayer distancebetween the individual layers is increased and this may cause aninterlayer separation. Thus, adding the resulting product into a solventand agitating the same may bring forth exfoliation to provide RuO_(2+x)nanosheets.

In an embodiment, the exfoliation of the alkali metal ruthenium oxidemay be carried out using at least two types of intercalating compoundshaving different sizes. For example, in some embodiments, the protonatedalkali metal ruthenium oxide may be treated with a first intercalanthaving a small size and a second intercalant having a large size.Examples of the at least two intercalant compounds having differentsizes may include a tetramethylammonium compound (e.g.,tetramethylammonium hydroxide), a tetraethylammonium compound (e.g.,tetraethylammonium hydroxide), a tetrapropylammonium compound (e.g.,tetrapropylammonium hydroxide), a benzyl trialkyl ammonium compound(e.g., benzyl trimethylammonium hydroxide), a tetrabutylammoniumcompound (e.g., tetrabutylammonium hydroxide), or a combination thereof,but it is not limited thereto. Examples of the first intercalant havinga small size may include tetramethylammonium hydroxide,tetraethylammonium hydroxide, or a combination thereof. Examples of thesecond intercalant having a large size may include tetrabutylammoniumhydroxide, benzyl trimethylammonium hydroxide, or a combination thereof.

The ruthenium oxide nanosheets thus obtained do not have a suitablesheet resistance. For example, the sheet resistance of the rutheniumoxide nanosheet is about 23,000 ohm/sq., as calculated by acomputational simulation. Therefore, it is desirable to enhance theconductivity of the ruthenium oxide nanosheets for the improvement ofthe electrical conductor including the ruthenium oxide nanosheet.

In some embodiments, the ruthenium oxide nanosheet is surface-doped witha doping element including a halogen, a chalcogen, a Group 15 element,or a combination thereof, so that the ruthenium oxide nanosheet mayprovide enhanced electrical conductivity and thereby provide a decreasedlevel of sheet resistance. The surface doping may be carried out byallowing the doping element to react with a surface of the nanosheet viaa thermochemical treatment (e.g., a hydrothermal treatment). As a resultof the thermochemical treatment, a local composition change may occur onthe surface of the ruthenium oxide nanosheet without causing anysubstantial change in the crystal structure of the nanosheet. Therefore,the surface of the ruthenium oxide nanosheet may undergo changes incharge distribution and charge movement, which results in a decreasedlevel of sheet resistance of the nanosheets.

The thermochemical treatment used for the surface doping may be carriedout on an intermediate product such as a hydrate of the alkali metalruthenium oxide (e.g., M_(a)RuO_(2+x)nH₂O) (see A of FIG. 1A), or aprotonated alkali metal ruthenate hydrate (e.g., H_(a)RuO_(2+x)nH₂O(0≤x≤0.5)) (see B of FIG. 1B), or on the ruthenium oxide nanosheet (seeC of FIG. 10).

The thermochemical treatment may include hydro-thermally treating theintermediate product or the ruthenium oxide nanosheet in the presence ofa compound including the aforementioned doping element (hereinafter,also referred to as a precursor) at a temperature of at least about 100°C.

The precursor may include a ruthenium halide such as RuCl₃, RuF₃, RuI₃,RuBr₃, or the like, a ruthenium chalcogenide such as RuS₂, RuSe₂, RuTe₂,or the like, an alkali metal halide such as AF, ACl, ABr, Al (A=Li, Na,K, Rb, Cs), or the like, an ammonium halide NH₄D (D=F, Cl, Br, I), or aruthenium-Group 15 element compound such as RuN, RuP, RuAs, RuSb, RuBi,or the like.

As a type of the thermochemical reaction, the hydro-thermal treatmentmay be carried out at a predetermined temperature and pressure. Thetemperature of the hydro-thermal treating may be selected appropriatelyin light of the pressure that the reactor can endure. For example, thetemperature may be greater than or equal to about 100° C., greater thanor equal to about 110° C., greater than or equal to about 120° C.,greater than or equal to about 130° C., greater than or equal to about140° C., greater than or equal to about 150° C., greater than or equalto about 160° C., or greater than or equal to about 170° C. Thetemperature may be less than or equal to about 250° C., or less than orequal to about 200° C. The time for the hydrothermal treatment is notparticularly limited and may be selected in light of other conditions.For example, the time for the thermochemical treatment (e.g., thehydrothermal treatment) may be greater than or equal to about 30 minutes(min), for example, greater than or equal to about 40 min, greater thanor equal to about 50 min, greater than or equal to about 1 h, or greaterthan or equal to about 24 h, but it is not limited thereto.

In a reaction medium (e.g., water) of the thermochemical treatment(e.g., the hydrothermal treatment), the concentration of the precursormay be controlled appropriately and is not particularly limited. Theconcentration of the precursor may be greater than or equal to about0.01 moles per liter (mol/L), but it is not limited thereto. Forexample, the concentration of the precursor may be less than or equal toabout 10 mol/L, but it is not limited thereto.

The pressure of the hydrothermal treatment is not particularly limitedand may be selected appropriately based upon the type of the precursor,the reaction medium, the pressure limit of the reactor, and the like.For example, the pressure of the hydrothermal treatment may be greaterthan or equal to about 1 atmosphere (atm), for example, greater than orequal to about 2 atm, greater than or equal to about 3 atm, greater thanor equal to about 4 atm, or greater than or equal to about 10 atm, butit is not limited thereto. For example, the pressure of the hydrothermaltreatment may be less than or equal to about 12 atm or less than orequal to about 10 atm, but it is not limited thereto.

As a result of the thermochemical treatment, the halogen, the chalcogen,and/or the Group 15 element (e.g. the doping element) may besurface-doped and thereby be present in the form of an ionic species, asurface-bound reactive group, an oxyhalide, an oxychalcogenide, or acombination thereof. The ruthenium oxide nanosheets surface-doped withone or more of the aforementioned elements may exhibit improvedelectrical conductivity and thus hold a potential to be utilized in aflexible electrode material for a transparent electrode.

The ruthenium oxide nanosheets may have an average lateral size, e.g., alength or width dimension in an in-plane direction, of greater than orequal to about 0.1 μm, for example, greater than or equal to about 0.5μm, greater than or equal to about 1 μm, greater than or equal to about2 μm, greater than or equal to about 3 μm, greater than or equal toabout 4 μm, greater than or equal to about 5 μm, or greater than orequal to about 6 μm, or about 0.1 μm to about 100 μm, or about 0.5 μm toabout 50 μm. The ruthenium oxide nanosheets may have an average lateralsize of less than or equal to about 100 μm, for example less than orequal to about 30 μm, less than or equal to about 20 μm, less than orequal to about 10 μm, less than or equal to about 9 μm, less than orequal to about 8 μm, or less than or equal to about 7 μm. When thelateral size of the nanosheets is about 0.5 μm to about 100 μm, thecontact resistance between the nanosheets may be decreased. The averagelateral size of the nanosheets may be determined in a Scanning ElectronMicroscopy analysis wherein a predetermined number (e.g., about 100) ofnanosheets are randomly selected and for each of the selectednanosheets, the largest value of a length or width dimension is measuredand an average of the measured values is calculated.

The ruthenium oxide nanosheets may have an average thickness of lessthan or equal to about 3 nm, for example less than or equal to about 2.5nm, or less than or equal to about 2 nm. The ruthenium oxide nanosheetsmay have an average thickness of greater than or equal to about 1 nm.When the average thickness of the ruthenium oxide nanosheets is lessthan or equal to about 3 nm, improved transmittance may be obtained.

In some embodiments, the ruthenium oxide nanosheet may have anelectrical conductivity, absorption coefficient, and sheet resistance asset forth in Table 1 when it is surface-doped with the doping element:

TABLE 1 Sigma (S/cm*) Alpha Rs (Ω/sq.) (conductivity) (absorptioncoefficient) (sheet resistance) Cl** 2.03 × 10⁵ 1.20 × 10⁵ 58.8 *Siemenspercentimeter (S/cm) **present in an amount of about 8.3 atomic percent(at %) with respect to a total combined amount of Cl and Ru.

When the ruthenium oxide nanosheet is surface-doped with the dopingelement, it may have a structure as schematically illustrated in FIG. 2.

The electrical conductor of the embodiments may include a secondconductive layer that is disposed on the first conductive layer andincludes a plurality of electrically conductive metal nanowires.

The electrically conductive metal nanowire included in the secondconductive layer may comprise silver (Ag), copper (Cu), gold (Au),aluminum (Al), cobalt (Co), palladium (Pd), or a combination thereof(e.g., an alloy thereof or a nanometal wire having two or more segmentsof different materials). For example, the electrically conductive metalnanowire may include a silver nanowire.

The electrically conductive metal nanowire may have an average diameterof less than or equal to about 50 nanometers (nm), for example less thanor equal to about 40 nm, or less than or equal to about 30 nm, or about1 nm to about 50 nm, or about 5 nm to about 25 nm. The length of theelectrically conductive metal nanowire is not particularly limited, andmay be appropriately selected considering the diameter. For example, theelectrically conductive metal nanowire may have a length of greater thanor equal to about 1 micrometer (μm), greater than or equal to about 2μm, greater than or equal to about 3 μm, greater than or equal to about4 μm, or greater than or equal to about 5 μm, or about 1 μm to about 100μm, or about 2 μm to about 50 μm, and is not limited thereto. Accordingto another embodiment, the electrically conductive metal nanowire mayhave a length of greater than or equal to about 10 μm, for examplegreater than or equal to about 11 μm, greater than or equal to about 12μm, greater than or equal to about 13 μm, greater than or equal to about14 μm, or greater than or equal to about 15 μm. The electricallyconductive metal nanowire may be fabricated according to any suitablemethod and may be a suitable commercially available metal nanowire. Thenanowire may include a polymeric coating on a surface thereof, such as acoating including polyvinylpyrrolidone.

Various efforts have been made to develop a flexible transparentelectrode material having excellent electrical conductivity and which istransparent in the visible light range. Metals may have high electrondensity and high electrical conductivity. However, most metals tend toreact with oxygen in air to form an oxide on a surface of the metalresulting in a greatly reduced electrical conductivity. Attempts havebeen made to reduce surface contact resistance using a ceramic materialhaving good conductivity and showing reduced surface oxidation. However,the currently available conductive ceramic materials (such as ITO)suffer from unstable supply of raw materials. Moreover, ceramicmaterials show minimal electrical conductivity compared to a metal, andalso, their flexibility tends to be poor. Since graphene as a layeredmaterial is reported to have it desirable electrical conductiveproperties, much research has been conducted regarding the use of asingle atom layer thin film of a layered structure material having weakinterlayer bonding force. For example, there have been attempts to usethe graphene as a substitute material for the indium tin oxide (ITO)having poor mechanical properties. However, the graphene has a highabsorption coefficient and thus is unable to provide a satisfactorylevel of light transmittance and cannot be used with a thickness ofgreater than or equal to about 4 layers. Transition metaldichalcogenides having a layered crystal structure may show comparabletransmittance when prepared as a thin film, but they have semiconductorproperties and thus have insufficient electrical conductivity to be usedas an electrically conductive film.

In contrast, the ruthenium oxide nanosheets surface-doped with a dopingelement, such as the halogen, the chalcogen, and/or the Group 15element, may provide improved electrical conductivity and enhanced lighttransmittance, as well as contributing to the flexibility of theprepared electrical conductor, and thus may be used to prepare aflexible electrical conductor, e.g., a flexible transparent conductivefilm.

The first conductive layer, including the aforementioned ruthenium oxidenanosheets, may include a discontinuous layer including an open spacebetween at least two of the ruthenium oxide nanosheets, and the area ofthe open space based on the total area of the first conductive layer maybe less than or equal to about 50%, for example less than or equal toabout 40%, less than or equal to about 30%, less than or equal to about20%, or less than or equal to about 10%, or about 1% to about 50%, orabout 5% to about 40%, based on a total area of the first conductivelayer. In order to obtain the area ratio of the open space, for example,a Scanning Electron Microscopic image of the first conductive layerincluding nanosheets disposed to have an open space is obtained and thearea of the open space (i.e., the portion not having the nanosheets inthe first conductive layer) is determined and is divided with the totalarea of the first conductive layer to provide an area ratio. In theelectrical conductor, a conductive metal nanowire, e.g., a silvernanowire, may be positioned to extend over the open space of the firstconductive layer.

In an embodiment, the first conductive layer is a discontinuous layercomprising spatially separated ruthenium oxide nanosheets of theplurality of ruthenium oxide nanosheets, and the ruthenium oxidenanosheets cover at least about 50%, about 50% to about 99%, about 60%to about 95%, or about 70% to about 90% of a total area of the firstconductive layer.

Formation of the first conductive layer and the second conductive layermay be carried out by any suitable method capable of forming a layer,and is not particularly limited.

In some embodiments, the first conductive layer including the rutheniumoxide nanosheets is formed on a substrate and the second conductivelayer including the conductive metal nanowires is formed on a surface ofthe first conductive layer. In this case, the substrate may be disposedon a surface of the first conductive layer opposite to the secondconductive layer.

The substrate may be a transparent substrate. A material of thesubstrate is not particularly limited, and it may be a glass substrate,a semiconductor substrate (e.g., Si), a polymeric substrate, or acombination thereof, or may be a substrate laminated with an insulationlayer and/or a conductive layer. For non-limiting examples, thesubstrate may include an inorganic material, such as an oxide glass or aglass, a polyester, such as polyethylene terephthalate, polybutyleneterephthalate, or polyethylene naphthalate, polycarbonate, an acrylpolymer, a cellulose or a derivative thereof, a polymer such as apolyimide, or organic/inorganic hybrid material, or a combinationthereof. The acryl polymer includes any polymer derived frompolymerization of an acryl or a methacryl monomer, e.g., acrylonitrile,methacrylonitrile, acrylamide, methacrylamide, acrylic acid, methacrylicacid, or an ester of acrylic or methacrylic acid.

The thickness of the substrate is also not particularly limited, and maybe appropriately selected according to the desired final product. Forexample, the substrate may have a thickness of greater than or equal toabout 0.5 μm, for example greater than or equal to about 1 μm, orgreater than or equal to about 10 μm, but is not limited thereto. Thethickness of the substrate may be less than or equal to about 1 mm, forexample less than or equal to about 500 μm, or less than or equal toabout 200 μm, but is not limited thereto. An additional layer (e.g., anundercoat) may be disposed between the substrate and the conductivelayer, if desired (e.g., for controlling a refractive index).

The first conductive layer or the second conductive layer may be formedby applying an appropriate coating composition (including the nanosheetsor the nanowires) on a substrate or a first conductive layer,respectively, and removing the solvent. The coating composition mayfurther include an appropriate solvent (e.g., water, an organic solventmiscible with water or immiscible with water, or the like), a binder,and a dispersing agent (e.g., hydroxypropyl methylcellulose (HPMC)).

For example, an ink composition including the metal nanowires may beprepared using any suitable method, or a commercially available productmay be used. For example, the ink may have the composition set forth inTable 2.

TABLE 2 Material Amount Conductive Conductive metal (e.g., Ag) nanowire 5 to 40 wt % metal aqueous solution (conc.: about 0.001 to about 10.0wt % conductive metal nanowires) Solvent Water 20 to 70 wt % Alcohol(ethanol) 10 to 40 wt % Dispersing Hydroxypropyl methyl cellulose (HPMC) 1 to 10 wt % agent aqueous solution (conc.: about 0.05 to about 5 wt %HPMC) * wt % is weight percent

For example, the coating composition including the aforementionedruthenium oxide nanosheets may be an aqueous solution including thecomponents in Table 3, but is not limited thereto.

TABLE 3 Material Amount Conductive RuO_(2+x) aqueous solution 30 to 70wt % material (concentration: 0.001-10.0 g/L, for example, about 0.01g/L to about 10 g/L, or about 0.5 g/L to about 2 g/L) Solvent Water 10to 50 wt % Isopropanol  1 to 20 wt % Dispersing Hydroxypropylmethylcellulose aqueous  5- to 30 wt % agent solution (about 0.05 wt %to about 5 wt %)

In some embodiments, when the concentration of the ruthenium oxidenanosheets in the aqueous solution is greater than about 0.001 gram perliter (g/L), a transparent conductor may be prepared to have a desiredelectrical conductivity by including a sufficient number of RuO_(2+x)nanosheets. When the concentration of the nanosheet aqueous solution isless than about 10 g/L, a transparent and flexible conductor may beprepared without any substantial loss of transparency or flexibility. Inaddition, in order to increase a dispersibility of RuO_(2+x) nanosheets,the RuO_(2+x) nanosheet solution may include a dispersing agent, such asa hydroxypropyl methyl cellulose (HPMC) aqueous solution. Theconcentration of the HPMC aqueous solution may be from about 0.05 weightpercent (wt %) to about 5 wt %, based on a total weight of the solution.In some embodiments, such ranges make it possible to maintain thedispersion of the RuO_(2+x) nanosheets in the solution without causingany adverse effects due to the presence of organic substances, forexample, a decrease in electrical conductivity or a decrease intransmittance.

The composition may be applied onto a substrate, or optionally, on thefirst or second conductive layer, and then may be dried and/orheat-treated if desired to produce the conductive layer. The coating ofthe composition may be performed by various methods, including forexample, bar coating, blade coating, slot die coating, spray coating,spin coating, gravure coating, inkjet printing, or a combinationthereof. The nanosheets may contact each other to provide an electricalconnection. When the prepared nanosheets are physically connected toprovide as thin a layer as possible, it may possible to further improvetransmittance.

The first conductive layer and/or the second conductive layer mayinclude an organic binder for binding the nanowires and/or thenanosheets. The binder may play a role in appropriately adjustingviscosity of the composition for a conductive layer or enhancingadherence of the nanosheets on the substrate. Examples of the binder mayinclude, but are not limited to, methyl cellulose, ethyl cellulose,hydroxypropyl methyl cellulose (HPMC), hydroxypropyl cellulose (HPC),xanthan gum, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP),carboxylmethyl cellulose, hydroxyethyl cellulose, or a combinationthereof. An amount of binder may be appropriately selected by the personof skill in the art without undue experimentation, and is notparticularly limited. In non-limiting examples, an amount of the bindermay be about 1 to about 100 parts by weight, based on 100 parts byweight of the nanosheets, (or the nanowires, in the case of the secondconductive layer).

The electrical conductor may further include an overcoating layer (OCL)including a thermosetting resin, an ultraviolet (UV) light-curableresin, or a combination thereof, on at least one of the first conductivelayer and the second conductive layer. Examples of the thermosettingresin and the UV light-curable resin for the OCL are known in the art.In some embodiments, the thermosetting resin and the UV light-curableresin for the OCL may include urethane (meth)acrylate, aperfluoropolymer having a (meth)acrylate group, a poly(meth)acrylatehaving a (meth)acrylate group, an epoxy (meth)acrylate, or a combinationthereof. The overcoating layer may further include an inorganic oxidefine particle (e.g., a silica fine particle). A method of forming an OCLfrom the aforementioned materials on the conductive layer is also knownand is not particularly limited.

The electrical conductor having the aforementioned structure may havesignificantly improved conductivity and high light transmittance and mayprovide enhanced flexibility. The electrical conductor may have lighttransmittance of greater than or equal to about 81%, for example greaterthan or equal to about greater than or equal to about 83%, greater thanor equal to about 85%, 88%, or greater than or equal to about 89%, withrespect to light having a wavelength of 550 nm. The electrical conductormay have a sheet resistance of less than or equal to about 5,000 ohmspre square (Ω/sq), for example, less than or equal to about 3,000 Ω/sq,less than or equal to about 2,500 Ω/sq, less than or equal to about2,400 Ω/sq, less than or equal to about 2,300 Ω/sq, or less than orequal to about 2,200 Ω/sq as measured by four point probe method.

The sheet resistance may be less than about 100 ohms per square (Ω/sq),for example, less than or equal to about 90 Ω/sq, less than or equal toabout 80 Ω/sq, less than or equal to about 70 Ω/sq, less than or equalto about 60 Ω/sq, less than or equal to about 50 Ω/sq, less than orequal to about 40 Ω/sq, less than or equal to about 39 Ω/sq, less thanor equal to about 38 Ω/sq, less than or equal to about 37 Ω/sq, lessthan or equal to about 36 Ω/sq, or less than or equal to about 35 Ω/sq.

The electrical conductor may exhibit enhanced flexibility. For example,after being folded multiple times, the electrical conductor may have aresistance change that is significantly lower than a resistance changeof the electrical conductor including the nanowires only. In someembodiments, the electrical conductors may have a resistance change ofless than or equal to about 60%, for example, less than or equal toabout 50%, less than or equal to about 40%, or less than or equal toabout 30%, after folding 200,000 times at a curvature radius of 1millimeter (mm) (1R).

In some embodiments, a method of producing the aforementioned electricalconductor may include:

heat-treating a mixture of a metal oxide and an alkali metal to preparean alkali metal-substituted layered ruthenium oxide;

treating the alkali metal-substituted layered ruthenium oxide with anacidic solution to prepare a proton exchanged layered ruthenium oxide,wherein at least a portion of the alkali metal is replaced with aproton;

contacting the proton exchanged layered ruthenium oxide with a C1 to C20alkyl ammonium compound to prepare an alkyl ammonium-layered rutheniumoxide; and

mixing the alkyl ammonium-layered ruthenium oxide with a solvent toobtain an exfoliated ruthenium oxide nanosheet,

wherein the method further includes conducting a surface-doping toobtain a plurality of surface-doped ruthenium oxide nanosheets, and

wherein the surface doping includes adding the alkali metal-substitutedlayered ruthenium oxide, the proton exchanged layered ruthenium oxide,or the exfoliated ruthenium oxide nanosheet to an aqueous solutionincluding a precursor (e.g., a ruthenium halide, a rutheniumchalcogenide, an alkali metal halide, an ammonium halide, or aruthenium-Group 15 element compound) to form a mixture; and

heating the mixture at a temperature of greater than or equal to about100° C.

The surface doping may be conducted with respect to the alkalimetal-substituted layered ruthenium oxide, for example, by combining thealkali metal-substituted layered ruthenium oxide with the aqueoussolution to form the mixture and heating the mixture, and the method mayfurther include drying a surface-doped product (e.g. the heatedmixture).

The surface doping may be conducted with respect to the exfoliatedruthenium oxide nanosheet, for example, by combining the exfoliatedruthenium oxide nanosheet with the aqueous solution to form the mixtureand heating the mixture, and the method may further include dispersing asurface-doped product (e.g. the heated mixture) in a mixture of asolvent and an intercalant (e.g., an alkyl ammonium compound) forre-exfoliation (e.g., after a washing with distilled water and a vacuumdrying thereof).

Details of the alkali metal-substituted layered ruthenium oxide, theproton exchanged layered ruthenium oxide, the ruthenium oxide nanosheet,the hydrothermal treatment for surface doping, the precursor compoundare the same as set forth above.

Some embodiments provide a one dimensional (1 D)/two dimensional (2D)hybrid structure including a nanosheet layer and a nanowire layer,

wherein the nanosheet layer includes a plurality of ruthenium oxidenanosheets being surface-doped with a halogen, a chalcogen, and/or aGroup 15 element and the nanowire layer includes a plurality of aconductive metal nanowires,

wherein in the nanosheet layer, at least two nanosheets of the pluralityof ruthenium oxide nanosheets are in contact with each other to providean electrical path and the nanowire layer is in contact with at leasttwo ruthenium oxide nanosheets of the plurality of ruthenium oxidenanosheets.

Details of the nanosheet layer are the same as those of the firstconductive layer. Details of the nanowire layer are the same as those ofthe second conductive layer. The 1D/2D hybrid structure may be preparedin the same manner as the aforementioned electrical conductor.

In another embodiment, an electronic device includes the electricalconductor or the 1D/2D hybrid structure.

The electronic device may be a flat panel display, a touch screen panel,a solar cell, an e-window, an electrochromic mirror, a heat mirror, atransparent transistor, or a flexible display.

In an exemplary embodiment, the electronic device may be a touch screenpanel (TSP). The detailed structure of the touch screen panel can bedetermined by one of skill in the art without undue experimentation. Theschematic structure of the touch screen panel is shown in FIG. 3.Referring to FIG. 3, the touch screen panel may include a firsttransparent conductive film 20, a first transparent adhesive film (e.g.,an optically clear adhesive (OCA)) 30, a second transparent conductivefilm 40, a second transparent adhesive film 50, and a window 60 for adisplay device, layered on a panel for a display device 10 (e.g., an LCDpanel). The first transparent conductive film 20 and/or the secondtransparent conductive film 40 may be the aforementioned electricalconductor or the hybrid 1D/2D structure.

In addition, while an example of applying the conductor to a touchscreen panel (e.g., a transparent electrode of TSP) is illustratedbelow, the conductor may be used as an electrode for other electronicdevices which include a transparent electrode without a particularlimit. For example, the conductor may be applied as a pixel electrodeand/or a common electrode for a liquid crystal display (LCD), an anodeand/or a cathode for an organic light emitting diode device, or adisplay electrode for a plasma display device.

Hereinafter, an embodiment is illustrated in more detail with referenceto examples. These examples, however, are not in any sense to beinterpreted as limiting the scope of this disclosure.

EXAMPLES

Measurement

[1] Measurement of Sheet Resistance:

Measuring equipment: Mitsubishi loresta-GP (MCP-T610), ESP type probes(MCP-TP08P)

Sample size: width about 20 cm×length about 30 cm

Measurement of sample: average value obtained from at least 9 separatemeasurements

[2] Measurement of Light Transmittance:

Measuring equipment: NIPPON DENSHOKU INDUSTRIES (NDH-7000 SP)

Sample size: width about 20 cm×length about 30 cm

The wavelength of light from the light source: 550 nm

Measurement of sample: average value obtained from at least 9 separatemeasurements

[3] Measurement of Haze:

Measuring equipment: NIPPON DENSHOKU INDUSTRIES (NDH-7000 SP)

Sample size: width about 20 cm×length about 30 cm

Measurement of sample: average value obtained from at least 9 separatemeasurements

[4] Scanning Electron Microscopic (SEM) analysis and Energy-dispersiveX-ray spectroscopy (EDX) analysis are made by using FE-SEM (FieldEmission Scanning Electron Microscope), Hitachi (SU-8030).

[5] X-ray diffraction analysis is made by using MP-XRD X'Pert PRO(Phillips).

[6] X-ray Photoelectron Spectroscopic analysis is made by using QuanteraII XPS Scanning Microprobe.

Example 1: Preparation of Ruthenium Oxide Nanosheets

[1] K₂CO₃ and RuO₂ are mixed at a mole ratio of 5:8, and the mixture ispelletized. 4 grams (g) of the obtained pellet is introduced into analumina crucible and heated in a tube furnace at 850° C. for 12 hours(h) under a nitrogen atmosphere. The total weight of the pellet may bechanged within the range of 1 g to 100 g, if desired. Then, the furnaceis cooled to room temperature and the treated pellet is removed andground to provide a fine powder. An X-ray Diffraction Analysis andElectron Microscopic Analysis are made for the obtained find powder, andthe results thereof confirm that the powder includes a layered rutheniumoxide.

The obtained fine powder is washed with 100 milliliters (mL) to 4 liters(L) of water for 24 h, and then filtered to provide a powder, thecomposition of which is K_(0.2)RuO_(2.1).nH₂O (wherein n is about 0.1 to0.9).

The K_(0.2)RuO_(2.1).nH₂O powder is then introduced into a 1 molar (M)HCl solution and agitated for 3 days (d) and introduced again into a 0.5M H₂SO₄ aqueous solution and agitated for 2 d. The resulting product isfiltered to provide a powder of proton exchanged layered rutheniumoxide, the composition of which is H_(0.2)RuO_(2.1).nH₂O. A scanningelectron microscopic analysis and an EDX analysis are conducted for theobtained powder and the results are shown in FIG. 4A, FIG. 4B, and Table4. The results of FIG. 4A confirm that the H_(0.2)RuO_(2.1)nH₂O particlehas a plate shape. The results of FIG. 4B and Table 4 confirm that thepowder does not include chlorine (Cl).

TABLE 4 element Wt % At % C_(K) 1.25 5.90 O_(K) 13.01 46.05 Ru_(L) 85.7448.06 Cl_(K) 0.00 0.00

The results of X-ray diffraction analysis of the obtained powder areshown in FIG. 5.

[2] The proton exchanged layered ruthenium oxide powder and a RuCl₃powder are mixed at a mole ratio of 0.9:0.1 and the mixture is placed ina 50 mL container. 400 mL of distilled water is added to the container,which is then subjected to a hydrothermal treatment at a temperature ofabout 180° C. for 24 hours using an autoclave. After the completion ofthe hydrothermal treatment, the container is placed in an oven at 50° C.for drying and thereby the treated powder is obtained. An X-raydiffraction analysis, a scanning electron microscopic analysis, and anEDX analysis are carried out for the obtained powder and the results areshown in FIG. 5, FIG. 6A, FIG. 6B, and Table 5.

TABLE 5 Element Wt % At % C_(K) 1.42 6.06 O_(K) 15.77 50.37 Ru_(L) 80.9840.94 Cl_(K) 1.83 2.63

The results of FIG. 5 confirm that after the surface doping, thenanosheets do not contain re-precipitated RuCl₃ crystals. In addition,the results of FIG. 5 suggest that the surface doping does not bringforth any substantial changes in the crystal structure of the nanosheet.These results also suggest that the Ru³⁺ and Cl⁻ ions react with theH_(x)RuO_(2.1)nH₂O.

The results of FIG. 6A confirm that the obtained product is in the sameform of a plate particle as its original form. The results of FIG. 6Band Table 5 confirm that the hydrothermally treated nanosheets includethe chlorine (Cl).

[3] 1 g of the H_(0.2)RuO_(2.1) powder as hydrothermally treated withRuCl₃ is introduced into 250 mL of an aqueous solution of tetramethylammonium hydroxide (TMAOH) and tetrabutylammonium hydroxide (TBAOH), andagitated for greater than or equal to 10 d. In the aqueous solution, theconcentrations of TMAOH and TBAOH are TMA+/H⁺=5 and TBA⁺/H⁺=5,respectively. After completing all processes, the final solution iscentrifuged under the conditions of 2,000 revolutions per minute (rpm)for 30 minutes (min) to obtain exfoliated RuO_(2+x) nanosheets havingthe surface doped chlorine.

[4] The coating liquid including RuO_(2.1) nanosheets having the surfacedoped chlorine is prepared to have the following composition:

An aqueous dispersion of RuO_(2.1) nanosheets having the surface dopedchlorine: 2 g (concentration: about 1 g/L)

An aqueous solution of HPMC: (0.25%) 0.5 g

Isopropanol: 2.5 g

Water: 2 g

The RuO_(2.1) nanosheet coating liquid is bar-coated on a polycarbonatesubstrate and dried at 85° C. under an air atmosphere. The processes arerepeated several times to prepare several first conductive layers, eachhaving a different light transmittance.

The light transmittance and the sheet resistance of the obtained firstconductive layer (RuCl₃ treated RuO_(2.1) coated film) are measured andthe results are compiled in FIG. 7.

The XPS analysis for the obtained first conductive layer is shown inTable 6 (below) and in FIG. 8.

Comparative Example 1

[1] Ruthenium oxide nanosheets are prepared in the same manner as inExample 1, except that the hydrothermal treatment using the RuCl₃aqueous solution is not carried out.

[2] The first conductive layers having different light transmittance areprepared on a polycarbonate substrate in the same manner as in Example1, except that the ruthenium oxide nanosheets prepared in step [1] areused instead of the RuO_(2.1) nanosheets having the surface doped Cl(Example 1).

The light transmittance and the sheet resistance of the prepared firstconductive layer (Reference) are measured and the results are compiledin FIG. 7. The XPS analysis for the obtained first conductive layer isshown in Table 6 and FIG. 8.

The results of FIG. 7 confirm that the electrical conductor includingthe ruthenium oxide nanosheets with the surface-doped Cl (RuCl₃ treatedRuO_(2.1) coated film) has a sheet resistance of 9,006 ohm/sq. and alight transmittance of 94.1%, while the electrical conductor ofComparative Example 1 (Reference) has a sheet resistance of 37,000ohm/sq. and a similar level of light transmittance. These resultssuggest that the electrical conductor including the ruthenium oxidenanosheets with the surface-doped CL may exhibit a much lower sheetresistance than the electrical conductor including the ruthenium oxidenanosheets with no surface doping while having a similar level of lighttransmittance.

TABLE 6 Concentration of the atom (at. %) O1s Na1s S2p Cl2p Ru3p3RuO_(2.1) film 80.9 1.23 0.65 0 17.22 (Comp. 1) Cl:RuO₂ film 74.06 0.380 1.1 24.46 (EX 1)

Results of Table 6 and FIG. 8 confirm that the first conductive layer ofExample 1 includes Cl and that the first conductive layer of ComparativeExample 1 does not include Cl.

Example 2: Preparation of Ruthenium Oxide Nanosheets with Surface-DopedCl

[1] K₂CO₃ and RuO₂ are mixed at a mole ratio of 5:8, and the mixture ispelletized. 4 grams (g) of the obtained pellet is introduced into analumina crucible and heated in a tube furnace at 850° C. for 12 hours(h) under a nitrogen atmosphere. The total weight of the pellet may bechanged within the range of 1 g to 100 g, if desired. Then, the furnaceis cooled to room temperature, and the treated pellet is removed andground to provide a fine powder.

The obtained fine powder is washed with 100 milliliters (mL) to 4 liters(L) of water for 24 h, and then filtered to provide a hydrate powder,the composition of which is K_(0.2-0.25)RuO_(2.1).nH₂O.

[2] The hydrate powder and a RuCl₃ powder are mixed at a mole ratio of0.9:0.1 and the mixture is placed in a 50 mL container. 400 mL ofdistilled water is added to the container, which is then subjected to ahydrothermal treatment at a temperature of about 180° C. for 24 hoursusing an autoclave. After the completion of the hydrothermal treatment,the container is placed in an oven at 50° C. for 12 h in order toconduct drying and thereby the RuCl₃ treated K_(0.2-0.25)RuO_(2.1)powder is obtained.

[3] The RuCl₃ treated K_(0.2-0.25)RuO_(2.1) powder is then introducedinto a 1 molar (M) HCl solution and agitated for 3 days (d) andintroduced again into a 0.5 M H₂SO₄ aqueous solution and agitated for 2d. The resulting product is filtered to provide a powder of protonexchanged and RuCl₃ treated layered ruthenium oxide (RuCl₃ treatedH_(0.2)RuO_(2.1)). 1 g of the RuCl₃ treated H_(0.2)RuO_(2.1) powder isintroduced into 250 mL of an aqueous solution of tetramethyl ammoniumhydroxide (TMAOH) and tetrabutylammonium hydroxide (TBAOH), and agitatedfor at least 10 d. In the aqueous solution, the concentrations of TMAOHand TBAOH are TMA+/H+=5 and TBA+/H+=5, respectively. After completingall processes, the final solution is centrifuged under the conditions of2,000 revolutions per minute (rpm) for 30 minutes (min) to obtainexfoliated RuO_(2.1) nanosheets with the surface doped chlorine.

[4] The coating liquid including the exfoliated RuO_(2.1) nanosheetshaving the surface doped chlorine (Cl) is prepared to have the followingcomposition:

An aqueous dispersion of RuO_(2.1) nanosheets having the surface dopedchlorine: 1 g (concentration: about 1 g/L)

An aqueous solution of HPMC: (0.3 wt %) 0.5 g

Isopropanol: 3 g

Water: 1 g

The RuO_(2.1) nanosheet coating liquid is bar-coated on a polycarbonatesubstrate and dried at 85° C. under an air atmosphere. The processes arerepeated three to four times to provide a first conductive layer. Thefirst conductive layer may have a sheet resistance of about 8,000 to10,000 ohm/sq. and a light transmittance of about 96 to 97%.

Example 3: Preparation of Ruthenium Oxide Nanosheets with Surface-DopedCl

[1] K₂CO₃ and RuO₂ are mixed at a mole ratio of 5:8, and the mixture ispelletized. 4 grams (g) of the obtained pellet is introduced into analumina crucible and heated in a tube furnace at 850° C. for 12 hours(h) under a nitrogen atmosphere. The total weight of the pellet may bechanged within the range of 1 g to 100 g, if desired. Then, the furnaceis cooled to room temperature, and the treated pellet is removed andground to provide a fine powder.

The obtained fine powder is washed with 100 milliliters (mL) to 4 liters(L) of water for 24 h, and then filtered to provide a powder, thecomposition of which is K_(0.2)RuO_(2.1).nH₂O.

The K_(0.2)RuO_(2.1).nH₂O powder is then introduced into a 1 molar (M)HCl solution and agitated for 3 days (d) and introduced again into a 0.5M H₂SO₄ aqueous solution and agitated for 2 d. The resulting product isfiltered to provide a powder of proton exchanged layered rutheniumoxide, the composition of which is H_(0.2)RuO_(2.1).

1 g of the H_(0.2)RuO_(2.1) powder is introduced into 250 mL of anaqueous solution of tetramethyl ammonium hydroxide (TMAOH) andtetrabutylammonium hydroxide (TBAOH), and agitated for at least 10 d. Inthe aqueous solution, the concentrations of TMAOH and TBAOH areTMA+/H+=5 and TBA+/H+=5, respectively. After completing all processes,the final solution is centrifuged under the conditions of 2,000revolutions per minute (rpm) and 30 minutes (min) to obtain exfoliatedRuO_(2.1) nanosheets.

[2] The exfoliated RuO_(2.1) nanosheets and a RuCl₃ powder are mixed ata mole ratio of 0.9:0.1 and the mixture is placed in a 50 mL container.400 mL of distilled water is added to the container, which is thensubjected to a hydrothermal treatment at a temperature of about 180° C.for 24 hours using an autoclave.

After the completion of the hydrothermal treatment, the container isplaced in an oven at 50° C. for 12 h in order to conduct drying andthereby the RuCl₃ treated RuO_(2.1) nanosheet powder is obtained.

The RuCl₃ treated RuO_(2.1) nanosheet powder is introduced into amixture of distilled water (as a solvent) and TMAOH and TBAOH (as aintercalant, TMA+/H+=5 and TBA+/H+=5) and stirred for one day to conductre-exfoliation. As a result, RuO_(2.1) nanosheets with the surface dopedCl are obtained.

[4] The coating liquid including RuO_(2.1) nanosheets having the surfacedoped chlorine is prepared to have the following composition:

An aqueous dispersion of RuO_(2.1) nanosheets having the surface dopedchlorine: 1 g (concentration: about 1 g/L)

An aqueous solution of HPMC: (0.3%) 0.5 g

Isopropanol: 3 g

Water: 1 g

The RuO_(2.1) nanosheet coating liquid is bar-coated on a polycarbonatesubstrate and dried at 85° C. under an air atmosphere. The processes arerepeated three to four times to provide a first conductive layer. Thefirst conductive layer may have a sheet resistance of about 10,000 to12,000 ohm/sq. and a light transmittance of about 96 to 97%.

Example 4: Preparation of the Electrical Conductors Including theNanowire Layer and the Ruthenium Oxide Nanosheet Layer

[1] Ag nanowire containing coating liquid including the followingcomponents is prepared.

Ag nanowire aqueous solution (conc.; 0.5 wt %, the average diameter ofthe Ag nanowire=30 nm): 3 g

Solvent: water 7 g and ethanol 3 g

Binder: hydroxypropyl methyl cellulose aqueous solution (conc.: 0.3%)0.5 g

The Ag nanowire-containing coating liquid is bar-coated on the firstconductive layer (i.e., the layer of the ruthenium oxide nanosheets withthe surface doped Cl) prepared in Example 1 and then is dried at 85° C.under an air atmosphere for 1 min to produce an electrical conductor.

[3] The sheet resistance, the transmittance, and the haze of theelectrical conductor are measured in the same manner as set forth above.As a result, the sheet resistance is 32.42 Ω/sq, the transmittance is89.14%, and the haze is 1.41.

Example 5

[1] Ag nanowire containing coating liquid including the followingcomponents is prepared.

Ag nanowire aqueous solution (conc.; 0.5 wt %, the average diameter ofthe Ag nanowire=30 nm): 3 g

Solvent: water 7 g and ethanol 3 g

Binder: hydroxypropyl methyl cellulose aqueous solution (conc.: 0.3 wt%) 0.5 g

The Ag nanowire-containing coating liquid is bar-coated on apolycarbonate substrate and then is dried at 85° C. under an airatmosphere for 1 min to prepare a silver nanowire layer.

[2] The RuO_(2+x) coating liquid prepared in Example 1 is bar-coated onthe silver nanowire layer, and then is dried at 85° C. under an airatmosphere for 1 min to obtain an electrical conductor.

[3] The sheet resistance, the transmittance, and the haze of theelectrical conductor are measured. As a result, the sheet resistance is27.76 Ω/sq, the transmittance is 81.32%, and the haze is 1.76.

Example 6

The electrical conductor prepared in Example 4 is fixed on a flat bottomand urethane acrylate (manufactured by Seukyung Co., Ltd.) is coatedthereon using a wired bar and then is dried at room temperature for atleast one min. Then, the resulting product is dried in an oven at about100° C. for one min and then is irradiated with UV light using a UV lamp(wavelength: 365 nm, intensity: 800 millijoules per square centimeter(mJ/cm²)) for 15 sec to conduct a crosslinking polymerization of theacrylate (i.e., a curing process) and thereby form an over-coat layer.

The sheet resistance, the transmittance, and the haze of the electricalconductor are measured. As a result, the sheet resistance is 28.28 Ω/sq,the transmittance is 83.79%, and the haze is 1.35.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. An electrical conductor comprising: a conductivelayer comprising a plurality of ruthenium oxide nanosheets and aplurality of conductive metal nanowires, wherein at least one rutheniumoxide nanosheet of the plurality of ruthenium oxide nanosheets aresurface-doped with any of a halogen, a chalcogen, a Group 15 element,and a combination thereof.
 2. The electrical conductor of claim 1,wherein the halogen comprises F, Cl, Br, I, or a combination thereof,the chalcogen comprises S, Se, Te, or a combination thereof, and theGroup 15 element comprises N, P, As, or a combination thereof.
 3. Theelectrical conductor of claim 1, wherein the halogen, the chalcogen, orthe Group 15 element is present as an ionic species, a surface-boundreactive group, an oxyhalide, an oxy chalcogenide, or a combinationthereof.
 4. The electrical conductor of claim 1, wherein the pluralityof ruthenium oxide nanosheets have an average lateral size of greaterthan or equal to about 0.1 micrometers and less than or equal to about100 micrometers, and a thickness of less than or equal to about 3nanometers.
 5. The electrical conductor of claim 1, wherein theplurality of conductive metal nanowires comprises silver, copper, gold,aluminum, cobalt, palladium, or a combination thereof.
 6. The electricalconductor of claim 1, wherein the plurality of conductive metalnanowires have an average diameter of less than or equal to about 50nanometers and an average length of greater than or equal to about 1micrometer.
 7. The electrical conductor of claim 1, wherein theelectrical conductor is a transparent conductive film.
 8. The electricalconductor of claim 1, wherein the conductive layer is a discontinuouslayer comprising spatially separated ruthenium oxide nanosheets of theplurality of ruthenium oxide nanosheets, and wherein the ruthenium oxidenanosheets cover at least about 50% of a total area of the conductivelayer.
 9. The electrical conductor of claim 1, wherein the electricalconductor has a transmittance of greater than or equal to about 85% at athickness of a conductive layer of 100 nanometers or less, with respectto light having a wavelength of 550 nanometers, and wherein theelectrical conductor has sheet resistance of less than or equal to about1.2×10⁴ ohms per square.
 10. The electrical conductor of claim 1,wherein the electrical conductor has a resistance change of less than orequal to about 60% after folding 200,000 times at a curvature radius of1 millimeter.
 11. The electrical conductor of claim 1, wherein theconductive layer further comprises a binder.
 12. The electricalconductor of claim 1, wherein the electrical conductor further comprisesan overcoating layer comprising a thermosetting resin, an ultravioletlight-curable resin, or a combination thereof, and wherein theovercoating layer is disposed on the conductive layer.
 13. Theelectrical conductor of claim 1, wherein the electrical conductorfurther comprises a transparent substrate that is disposed on a surfaceof the conductive layer.
 14. A method of preparing the electricalconductor of claim 1, the method comprising: heat-treating a mixture ofa ruthenium oxide and an alkali metal compound to prepare an alkalimetal-substituted layered ruthenium oxide; treating the alkalimetal-substituted layered ruthenium oxide with an acidic solution toprepare a proton exchanged layered ruthenium oxide, wherein at least aportion of the alkali metal is replaced with a proton; contacting theproton exchanged layered ruthenium oxide with a C1 to C20 alkyl ammoniumcompound to prepare a C1 to C20 alkyl ammonium-layered ruthenium oxide;mixing the alkyl ammonium-layered ruthenium oxide with a solvent toobtain an exfoliated ruthenium oxide nanosheet; conducting a surfacedoping to obtain the plurality of surface-doped ruthenium oxidenanosheets; applying a composition comprising the plurality of thesurface-doped ruthenium oxide nanosheets on a surface of a substrate toform a conductive layer; and applying a composition comprisingconductive metal nanowires on a surface of the conductive layer, whereinthe surface doping comprises adding the alkali metal-substituted layeredruthenium oxide, the proton exchanged layered ruthenium oxide, or theexfoliated ruthenium oxide nanosheet to an aqueous solution comprising aruthenium halide, a ruthenium chalcogenide, an alkali metal halide, anammonium halide, or a ruthenium-Group 15 element compound to form amixture, and heating the mixture at a temperature of greater than orequal to about 100° C.
 15. The method of claim 14, wherein the surfacedoping is conducted with the alkali metal substituted layered rutheniumoxide, and wherein the method further comprises drying the plurality ofsurface-doped ruthenium oxide nanosheets.
 16. The method of claim 15,wherein the surface doping is conducted with the exfoliated rutheniumoxide nanosheet and wherein the method further comprises dispersing asurface-doped product in a mixture of a solvent and a C1 to C20 alkylammonium compound to prepare a re-exfoliated ruthenium oxide nanosheet.17. The method of claim 14, wherein the plurality of ruthenium oxidenanosheets have an average lateral size of greater than or equal toabout 0.1 micrometers and less than or equal to about 100 micrometers,and a thickness of less than or equal to about 3 nanometers.
 18. Anelectronic device comprising the electrical conductor of claim
 1. 19.The electronic device of claim 18, wherein the electronic device is aflat panel display, a touch screen panel, a solar cell, an e-window, anelectrochromic mirror, a heat mirror, a transparent transistor, or aflexible display.
 20. An electrode comprising the electrical conductorof claim
 1. 21. The electrode of claim 20, wherein the electrode is atransparent electrode, pixel electrode, a common electrode for a liquidcrystal display, an anode for an organic light emitting diode device, acathode for an organic light emitting diode device, or a displayelectrode for a plasma display device.